The present invention relates to the manual propulsion of boats. More particularly, the invention relates to a foldable manual propulsion unit for mounting on a variety of small boats. Even more particularly, the present invention relates to a rudder-like unit that is clamped to the transom of a small boat in much the same way as an outboard motor.
Small boats have been used since the beginning of civilization for transportation over the water. Examples of such boats abound, e.g. dinghies, sailboats, inflatable boats, punts, lifeboats, and the like, and each type or style may have certain specialized uses for which it is well adapted. For example, some boats have shallow drafts to enable them to easily maneuver in swampy areas, whereas some have deeper drafts to allow them to manage in heavy waves. Some boats are inflatable for compact storage, minimum weight, and convenience. Still others may exhibit specialized features for activities such as fishing, scuba diving, or pleasure boating.
There are numerous methods of achieving movement of such boats over the surface of the water. These methods employ various devices that may be conveniently divided for purposes of discussion into mechanical devices (diesel or gasoline engines used to turn underwater screws or above-the-surface propellers), wind-powered devices (primarily utilized by different configurations of sail), and manual devices (oars or paddles). Manual devices are used either for both primary movement or as a backup whenever the primary movement method is unavailable. The most frequently encountered backup method consists of the use of oars or paddles since they are inexpensive, relatively light, and compact, depending upon the construction. They are also relatively quiet, do not require an external fuel source such as an engine requires, and do not depend upon environmental conditions as does a sail.
A number of techniques have been developed for using oars and paddles. Traditionally, oars have been employed in pairs, one for each hand, and inserted into pivoting oar locks on either rail of the boat. The oar locks serve as fulcrums for coordinated reciprocal motion of the oars by an oarsman. The flattened ends of the oars are dipped into the water and the boat is propelled by a pushing or pulling motion against the water by the oarsman. This action requires a sturdy platform to serve as the base for the oar locks and thus is most suitable for boats with rigid sides, the tops of which are relatively close to the water to allow the oars to be dipped therein without excessive upward reaching by the oarsman. Inflatable boats have much softer sides that are wider than those of rigid-sided boats; oar locks in the form of tabs having holes for the oars are sometimes sewn into the upper surfaces of such inflatable boats, but their use is generally awkward. One basic problem with this method of using oars is that the oarsman is generally in a position facing rearward to the direction of travel.
Another technique involves the use of a single oar, or paddle. In one variation, both hands of the oarsman are placed on the paddle, which is dipped into the water from a side of the boat. This method is favored for canoes and other light craft, but the sides must be sufficiently low and thin to allow the paddle to be inserted into the water without excessive reaching on the part of the oarsman. Paddles have been used to propel inflatable boats also, but the width of the side pontoon comprising the sides of an inflatable boat may require the oarsman to excessively reach out laterally, which may in turn cause premature fatigue. In another variation, the paddle or oar is mounted at the stem of a boat and worked from side to side to move the boat forward, much like the tail fin of a fish. For example, this method is employed by Venician gondoliers to propel the craft through narrow canals in Venice. Sculling is generally performed at the stern of the boat, although certain mechanical devices scull from amidships through the bottom of the boat, as will be seen presently.
Inflatable boats are quickly becoming the most popular small craft on the water. Their popularity is due in part to their affordability, stability, and comfort. Because of the problems discussed above, they are primarily propelled from the stem by an outboard motor. However, use of an outboard motor is often difficult or undesirable because of the weight and noise of the motor and the necessity for an accompanying gasoline tank, which takes up space within the craft. There is also the possibility of motor failure, which may leave occupant stranded. Paddles are often provided for emergency purposes, but, in order to save weight and space, they are generally flimsy and of insufficient length to enable them to be used for any significant period of time. Furthermore, they are difficult to use when mounted against the soft sides of the inflatable pontoons.
Paddles and oars do have another advantage over motors, in that they do not project downwardly in the water to any significant depth and, if they do encounter the bottom or some rigid object, they will yield before breaking. An outboard motor, on the other hand, rigidly projects a given depth below the bottom of the boat. When it encounters a rigid object, such as the floor of the body of water, either the pin holding the propeller will shear off to prevent damage to the propeller or the motor will kick back over the transom. Paddles and oars are more useful in such shallow situations.
Inflatable boats and other small craft have been particularly popular with scuba divers. During diving excursions, those participating in these underwater pastimes may easily enter the water by rolling off the sides of the pontoons of an inflatable boat. This method of entering the water is especially useful, given the heavy tanks and other equipment that the divers must carry. After a dive and upon reentering an inflatable or other small craft from the water, the divers are often fatigued and find it difficult to climb back into the boat. Small ladders of aluminum or rope construction are frequently used to assist the divers to reenter the boat. Such ladders do not work well on the sides of inflatable boats because of the lack of a stable platform for mounting and they do not work well at the more rigid stem because of the presence of motor or boat steering components.
Numerous devices have been proposed to implement the sculling method of propulsion with small boat. One such device consists of a vertically fin situated on a shaft projecting through the floor of the boat and under the bottom to propel and steer the boat in any direction. It has a horizontal arm mounted at the top of the shaft so that the shaft, and thus the fin, may be moved back and forth using either arm or leg power. The vertical fin is hinged to raise up without breaking when encountering an obstruction or the floor of the water way. This device is suited for rigid boat structures and must be permanently configured with the craft, since a water seal must be installed around the vertical shaft where it penetrates the bottom of the boat. Such devices are useful where portability and economy of space are not a criteria for use. One similar device uses pulleys rather than extending arms to actuate the fin. Another such device uses a tread system rather than pulley to transfer manual power from foot pedals to the vertical fin. At least one recreational lounging craft employs a sculling propulsion method that is actuated by foot power that oscillates a flexible fin to propel the device, but again, such devices are integral to the craft.
Thus, it can be seen that there is a need for a manual propulsion apparatus for small boats that is removable and portable. It should occupy a minimal amount of space when not installed and not in use, as when it is used as an emergency device rather than as the primary propulsion device. It should be adaptable for use with more than one design of boat, easy to operate for long periods of time, and downwardly adjustable for clearance in shallow water operation. Optionally, it should also provide a means for assisting persons in the water to reenter the boat.